Ultra high frequency amplifying circuit



y 1949- M. J. o. STRUTT ETAL 2,476,392

ULTRA HIGH FREQUENCYAMPLIFYING CIRCUIT Filed Feb. 14, 1947 -M...LO}STRU"'I"1 & A.VAN.D ER ZlEL INVENTORS AGENT Patented July 19, 1949 UNITED STATES PATENT OFFICE ULTRA HIGH FREQUENCY AMPLIFYING CIRCUIT Application February 14, 1947, Serial No. 728,708 In the Netherlands September 2, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires September 2, 1964 7 Claims.

This invention relates to an ultra-high frequency amplifying circuit comprising a discharge tube which contains at least a cathode, a control grid and an output electrode and in which the oscillations to be amplified are supplied to an input impedance connected between the control grid and the cathode, whereas the amplified oscillations are obtained from an output impedance interposed between the output electrode and the control grid.

In the case of high frequency amplifiers use is generally made of the so-called common cathode circuit, in which the input impedance is arranged between the control grid and the cathode and the output impedance between the output electrode and the cathode of the amplifier valve. When amplifying ultra-high frequencies it may, however, be advantageous to arrange the output impedance between the output electrode and the control grid, the latter being connected, so far as high-frequency currents are concerned, to a point of constant potential (earth) such circuit arrangement being referred to as a common grid circuit. There are bands of very high frequencies in which the common grid circuit has a lower input damping thanthe common cathode circuit, but even so the input damping of the common grid circuit in such frequency bands may be comparatively high, so that it is desirable to provide for means by which the input damping is further reduced.

According to the invention, for this purpose that part of the control grid circuit that does not form part of the high frequency connection between the output electrode and the cathode includes a predominantly capacitative impedance which is so proportioned that the damping produced by the tube on the input impedance is substantially neutralised.

The said predominantly capacitative impedance is preferably constituted by a Lecher line connected between the control grid and a point of constant potential.

As an alternative, a highly efiicient embodiment of the invention may be secured, if the said predominantly capacitative impedance is constituted by a condenser which is housed in the discharge tube and shunted by a leak resistance and which is connected by connections as short as possible on the one hand to the control grid and on the other hand to a tapping point, from which issue two current supply leads one of which is connected to the input impedance and the other to the output impedance.

In order that the invention may be clearly I 2 understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, in which some few embodiments are illustrated.

In the drawing:

Fig. 1 is a schematic circuit diagram of one embodiment of an amplifier in accordance with the invention,

Fig. 2 is a schematic circuit diagram of another embodiment of an amplifier in accordance with the invention, and

Fig. 3 is a schematic circuit diagram of yet another embodiment.

Figure 1 shows an amplifier circuit for ultrahigh frequency oscillations which comprises an amplifier valve I. This valve contains a cathode 2, a control grid 3, a screening grid 4, a suppressor grid 5 connected to the cathode, and an anode 6. The control grid 3 and the cathode 2 have arranged between them an input impedance 1 to which the oscillations to be amplified are supplied, whereas the anode 6 and the controlgrid llhave connected between them an output impedance 8 from which the amplified oscillations are obtained. The connecting point between the impedances 1 and 8 isearthed.

According to the invention, the control grid 3 and earth have arranged between them a condenser 9 which is proportioned in such manner that the dampin produced by the tube on the input impedance I is substantially neutralised. For this purpose, the condenser 9 must in practice have a capacity which is of the same order of magnitude as or several times higher than the control grid-cathode capacity.

Figure 2 shows an embodiment of the invention in which the condenser 9 is replaced by a Lecher line In whose length is chosen to be such that it has a capacitative input impedance. The input impedance 1 and the output impedance 8 are also replaced by Lecher lines, which are designated II and I 2 respectively.

Figure 3 shows an embodiment of the invention in which the condenser is housed jointly with a leak resistance IS in the discharge tube and connected through short connecting wires on the one hand to the control grid 3 and on the other hand to a tapping point l4. From the tapping point issue two supply leads one of which leads to the input impedance (in the present case the Lecher line I I) and the other to the output impedance (in the present case the Lecher line 12).

What we claim is:

1. A high frequency amplifying system comprising an electron discharge device having a cathode, a control grid, a screen grid and an anode, an'input impedance having one end connected to said cathode, an output impedance hav ing one end connected to said anode, the other ends of said impedances being interconnected, a predominantly capacitive impedance'..iconnected between said interconnection and said control grid and having a value substantially neutralizing the damping effect of saidldevice .on said innit impedance, and means effectivelycoupling said screen grid to ground.

2. A high frequency amplifying system comprising an electron discharge 'device having a cathode, a control grid, a screen gridand an anode, a tuned input impedanceeconnecting said cathode to ground, a tuned output impedance coupling said anode to ground, a predominantly capacitive impedance connecting said control grid to ground and having a value substantially neutralizing the dampingzreffectofi said device on said input impedanca'and. means:effectively coupling said'screen gridftoiground forhigh 'frequencies.

3. A high frequency amplifyingi'system.comprising an electroni'discharge device'having a cathode, a control:- gridj a.::scre'en: grid' and: an anode, a tuned input impedance connectingsaid cathode to ground, l; artunedi output :inipe dance couplingcsaid anode tOTIgI'OllIld; a capacitor connecting said control grid to ground and having a valuesubstantially-neutralizing'therdamping effect of said device on said input'impedance, and means effectively coupling saidscreenr grid to groundifor highifrequencies.

4. .A; "high frequency: amplifying. system comprising an electron discharge device-having a cathode, anontrolgrid, a screen grid and an anode; a'fltunedinput impedance connecting said cathode to "ground; aitunedoutput impedance coupling-said anodeto'ground; a Lecher line having alength at-which'saidiineacts: as-a capacitanceiconnecting saidcontrol grid: to ground and having; a value substantially neutralizing the damping effect of said-device on saidi-nput-impedance, and meansr effectively -coupling said screen grid to groundafor high'frequencies.

vlthe operating frequency and connected between said cathode and ground, an output Lecher line tuned'to' the operating frequency and connected -between said anode and ground, an auxiliary Lecher line having a length at which said line acts as a capacitance at the operating frequency, said auxiliary line. being-connected between said control grid and ground and having a capacitive value substantially neutralizing the damping efiect of said device on said input Lecher line, and means effecting by-passing said screen grid to ground at M the operating frequency.

6. .Anamplifying system adapted to operate at a high frequency comprising an electron discharge device including within an envelope a cathode, a control grid, a screen grid and an anodef an input impedance. connected between saidtcathode and said :controlvgridy-an output timpedance :connected between said; anode and said control :grid, a capacitor;connectedinyparallel with a grid leak disposed ,within. the envelope of said device andelectricallyinterposed" between said control grid landxsaid'input. and output impedances, said capacitor; having a .value I substantially neutralizing therdampingefiectofisaid device on said input impedance, and meansf'effectively by-passing said screen grid to ground at the operating frequency.

7,An,-..-an*angement? asset- .forth inpclaim 6 wherein saidJinput-i and outputdmpedances are eachconstituted by aLecher line tuned to-the operating frequency.

, JULIUS OTTO STRUTT.

ALDERT VAN' DER ZIEL.

7 REFERENCES CITED Thefollowing references are of record in'the file of'this patent:

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